Countercurrent contact apparatus



Dec. 16; 1941. v w. J. 'D. VAN DIJCQK I 2,266,521

COUNTERGURRENT CONTACT APPARATUS Filed Dec. 9, 1939 Inventor: Wfllem J9, nnus Dom'an'ucus vonpijck 6g his AH'orne Patented Dec. 16, 1941 COUNTERCURRENT CONTACT APPARATUS Willem Johannes Dominicus van Dijck, The

Hague, Netherlands, assignor to Shell Development Company, San Francisco, Calif., a corporation Of Delaware Application December 9, 1939, Serial No. 308,437

In the Netherlands December 14, 1938 9 Claims.

The invention relates to an apparatus for contacting continuously and countercurrently two non-miscible or only partly miscible liquids of different specific gravities such contacting being usually performed with the object of withdrawing one or more components from one liquid with the aid of the other liquid as, e. g., in extracting or washing operations, or with the object of subjecting one liquid to a chemical treatment with the other. The invention more particularly relates to improvements in an apparatus of the type wherein a horizontal, inclined, or vertical tubeor shell is provided with transverse perforated partitions, subdividing the shell into a connected series of alternating mixing and settling zones and wherein the two liquids pass through these mixing and settling zones in opposite directions; certain features of the invention may, however, also be employed in devices wherein the mixing and settling zones are not arranged in the same shell. The stirring devices present in each mixing zone in the preferred embodiment may be mounted on a common rotatable shaft extending in the longi-' tudinal direction of the tube or shell and turned by a pulley. H

An apparatus of this general type is described in United States Patent No. 2,154,713. It provides a settler between every two mixers, in which settler the separation of the liquid phases contained in the mixtures leaving the mixing zones should take place and from which the separatedliquids should be fed again to the mixing zones in such a manner that in all settling zones one liquid flows toward one end of the tube and the other liquid flows in the opposite direction. Because in such a device each intermediate settling zone receives mixtures from the two adjacent mixing zones and is in direct communication with both of these zones, it is unavoidable, especially if the stirring devices are capable of effecting an intensive circulation in the settler, not only that the liquid already treated in a mixing zone is returned to the same mixing zone-which inher'ently reduces the capacity of the apparatusbut also, what is even more objectionable, that this liquid is returned to the preceding settling zone and from there is allowed to enter the preceding mixing zone resulting in a decrease of the ehiciency of the treatment, per stage and thus in the case of extraction in a decrease of the sharpness of the separation.

It is an object of the invention to provide an apparatus of the type described wherein suitable structures, such as perforated walls, are provided in the settlers between any two mixing zones in such 'a manner that the above drawbacks of the usual countercurrent stirred column are obviated.

It is a further object of the invention to improve the structure of the partitions separating the mixing and settling zones, so as to improve the transfer'of material from and to the mixing zones.

Other objects of the invention will be apparent from a reading of this specification.

In subsequent discussion and in the claims: to avoid confusion the term wall has been usedto designate the structures which subdivide the settling zone whereas the term partition has been reserved to designate the structures which sepa rate the mixing and settling zones.-

The apparatus according to the invention, comprises a connected series of alternating mixing and settling zones arranged to cause the two liquids to pass in opposite directions through the mixing and settling zones countercurrently to one another and one or more walls in each intermediate settling zone arranged to subdivide the settling zone into at-least two'spaces, one space being in direct communication with only one of the-mixing zones adjacent to the said intermediate. settling zone, and another space beingin direct'eommunication onlywith the other mixing liquid flows through the opening at the lower level. By this arrangement mixing of mixtures from two different mixers and the return of a liquid to a preceding mixing or settling zone is minimized or obviated. The mixing and settling zones may be separateunits connected with conduits, but are preferably located within a single cylindrical shell as illustrated. 'Such a shell may be placed in any position, such as from O to from the horizontal, the only requirement being that the walls dividing the settling zones into spaces be not horizontal so as to permit openings in the walls to be located at different levels. This may, in certain installations, require that thewalls be not perpendicular to the axis of the shell.

Figure I is a sectional elevation view of one preferred embodiment of the invention. f

Figure II is a cross-sectional view taken on section line II--II of Figure I. v

Figure III is a fragmental sectional elevation view of a modified apparatus wherein two walls are provided in the settling zone.

Figure IV illustrates a fragmental section of an apparatus provided with modified partitions between mixing and settling zones.

Figure V is a cross-sectional view taken on section line VV of Figure IV showing the modified partition.

Figures VI, VIII and IX are sectional views similar to Figure V showing modified arrangements of the holes in the partitions.

Figure VII is a fragmental section of an apparatus similar to Figure IV illustrating a, further modification in the partitions wherein certain openings are omitted.

Referring to Figure I, I is an inclined cylindrical shell carried by suitable supports 2 and 3 and subdivided by partitions 4d, ib, 4c, 4d, 4a, 4b, 4c and 4d, etc., formed of perforated plates or sieves to provide alternating mixing and settling zones. Any suitable number of partitions may be provided, only four mixing zones 5d, 5b, 5a, 5b with intermediate settling zones 6 and 6 in addition to end zones I and 8 being illustrated. Walls 9 and 9' divide their respective settling zones into sub zones or spaces Illa, Illb, Illa and Illb. The walls 9 and 9' at the top and bottom are perforated by openings I la, I lb, I la and I I b respectively. The space Illa is in direct communication only with the mixing zone 5a while the space IIlb is in direct communication only with the mixing zone 5b.

A common shaft I2 carries agitators I3a, I3b', I3a and I311 such as propellers or stirring rods, and is turned by pulley I4 to provide mixing in the mixing zones.

Valves I5 and I5 control the feed to and. outflow from the end settling zone I while valves I1 and I8 similarly control the outflow from and feed to end settling zone 8.

Referring to Figure I, a light liquid A is fed from the left through valve I5 and a heavy liquid B from the right through valve I8. These liquids pass through the apparatus countercurrently, and are repeatedly contacted with each other in the mixing zones so as to interact the light liquid A leaving the apparatus through valve IT and the heavy liquid B through valve I5.

During the operation of the apparatus a mixture is thus continuously produced in the mixing zones, which mixture, owing to, inter alia, the centrifugal effect and the differences in specific gravity, moves to the adjoining settling zones in which separation takes place. The regions within the shell zones containing mixtures of liquids have been indicated diagrammatically in the drawing by dots, regions containing single phases being left unmarked. The mixture fed into the settling zone stratifies, i. e., the light liquid rises and the heavy liquid descends so that the mixture has above it the separated liquid A and below it the liquid B. The space Illa receives the mixture only from mixing zone 5a, and the space IOb receives the mixture only from mixing zone 51). Now it is the intention that of the stratified phases at the top only the A liquid should pass from the left-hand space Ina tothe placed slightly inclined, so as to obtain the displacement in the desired direction by a rising of the light and a falling of the heavy liquid, although such inclination is not essential.

The walls 9 and 9 perform two distinct functions: they prevent the mixing of the two mixtures of liquids from the spaces Illa and Illb, etc., which mixtures were produced in different mixing zones and are, therefore, in different stages of treatment; and they prevent the moving of the liquids separated from these mixtures by settling in the undesired direction, thereby preventing flow to a mixing or settling zone where the liquid in question is still in a previous stage of treatment. In other words, the perforated wall only enables mixing of the separated liquids in the direction in which the liquid in question flows through the apparatus. Thus, the light liquid A in space Illb, which is already in a further stage of treatment than that in Ilia, cannot return to space Ida, and thence to mixing zone 5a, in which case the efficiency of the treatment would be reduced.

Referring to Figure III, the construction is similar to that shown in Figure I, reference characters I, 4a, 5b, 4c, 4d, 5a, 5%), I2, I30 and I3b designating the same elements. In this modification the settling zone between the mixing zones 5d and 5b is provided with two walls Ila and 9b, thereby separating the settling zone into terminal spaces Ida and IOb (in direct communica-' tion with mixing zones 5a and 5b, respectively) and an intermediate space Iflc. The walls 9a and 9b are provided with holes Ila and Ilb, as described for Figures I and II.

The intermediate space I00 permits liquid entrained with the material flowing through the holes I la and I lb to settle out. Thus, the reavy liquid B moving to the left from the space IBb may contain an undesirable amount of the liquid A because the mixture in the space Iflb is not entirely quiescent. This entrained liquid A rises in the intermediate space Ific, wherein substantially no agitation obtains. The heavy liquid B which flows through the bottom opening III] of the wall 9a to the space Ida is thereby substantially free from the liquid A. In the same manner the light liquid A flowing from the space I80, I

is, in the space Iflc, freed from entrained liquid B.

The fewer superfluous circulation currents there are the more rapid will be the demixing or stratification in the settling zones. Circulation (1. e., two way flow) between a particular mixing zone and the adjacent settling zone is, of course, necessary, because only one of the two liquids should move from said settling zone to the next mixing zone, whereas the other liquid must return to the said particular mixing zone. For bringing about this necessary circulation inclination of the shell or provision of pumps are not necessary; the disturbance of the equilibrium due to the mixing is sufficient. Thus, this mixing produces in the mixing zone of a dispersion having a density intermediate the densities of the separated liquids A and B in the settling zone. The separated liquids therefore flow through the openings at top and bottom of the partitions 4a, etc., from the settling zones to the mixing zones, whilst the mixture flows at anintermediate level from the mixing zones to the settling zones. Owing to the centrifugal effect of the rotating stirring devices, however, the liquids in the mixing zone near the shaft l2 will be caused to flow radially outward in the mixing zone, drawing in material from the settling zone near the shaft.

This sets up a circulation in the settling zone in thegdirection from the circumference of the tube to'the center, as shown by the doubleheadedarrows inF'igure III. This superfluous circulation causes an increased consumption of energy and a decrease of the capacity of a given apparatus. Now according to theinvention one may preventthis superfluous circulation due to centrifugal effect by providing the connections between mixing zones and, settling zones in an.

otherwiselclosed partition at points substantially spaced from the shaft, preferably adjacent to the shell and at equal distances from the center line of the rotating shaft. In ordertomaintain the circulation resulting from the disturbance of the equilibrium by the mixing action, openings have been provided at least both at the level of the rotating shaft and above and below it. This is illustrated in Figures IV and V.

Referring to Figures IV and V, reference numbers I, 9, I2, I30. and [3b designate the same elements as in Figure I. Thedevice in these figures diiiers only in that the sieve-like partitions 4a, etc., are replaced by partitions I911, I91), I90, and lHd, which are imperforate except for the radial inlet openings 20a and 20b at the top and bottom and the radial outlet openings 2Ia andZIb at about the level .of the shaft l2. The distribution and shape of the radial openings is shown i Figure V.

The circulation of the mixture and of the separated liquids between the mixinggzone and the settling zone adjoining it are shown in Figures IV and V by the double-headed arrows, the fiow of the separated liquids between thespaces of the settling zone being shown by the singleheaded arrows. The mixture formed leaves the caused by the rotation of the stirrers I3a, l3b, etc., through these openings into the settling zone. It has been found that the radialslots offer great resistance to flow ina direction having a tangential aswell as an axial component with respect to the shell.

.It will be observed that the current in the upperleft-hand part of the settling zone in Figure IV andthat in the lower right-hand part both shown by the double-headed arrows are such as to cause the movement of the liquidA or B to counteract the movement required. to create a continuous flow of A or B through the whole apparatus. From this point of view it may,

therefore, in certain cases be better to omit the,

group ofupper inlet openings 20a of partitions I92: and [9d, and the group of lower inlet openings 20b of partitions lSa and [9c altogether, or to reduce their size or to provide them at a level nearer the center of the shaft.

. the openings 20a in partitions I91 and i9d and mixing zone through the openings 2Ia and Zlb situated at the level of the shaft and the separated liquids return to the mixing zone through the top and 'the'bottom'openings. If these currents are compared with those,,as shown in Figure III, caused by the centrifugal effect, it is found-that, on account of their direction, the

currents according. to Figures IV and V, are much more favorable with a view to creating a place of comparative quiescence and with pure liquids A and B atthe top and bottom, respectively, of the settling zone near wall 9; the dimensionsof the settling zone, measured in the direction of the shaft, may then be smaller.

The intensity of the circulation thus created by the disturbance of the equilibrium depends, besides on the difierence in specific gravity be? tween the two liquids, on the vertical distance between the outlet openings Zla and 2117 and the inlet opening. 20a, as well as on the vertical distance from the outlet opening to the inlet opening 201). If, with the openings 20a and 291) provided right at the top and at the bottom, this circulation should be too intensive, outlet openings 20a and 20b may be provided at levels nearer to the level of the outlet openings 2la' and Zib as shown in Figure VI.

One may also provide all the openings, not on the circumference of the partition, but at smaller equal distances from axis of the shell.

Attention may be drawn to the shape of the openings 20a, 20b, Zla and 2"; in partition I9a, etc., as shown in Figures V and VI; each of them consists of a number of radial slots. The object of this shape is to prevent propagation of the rotation of the liquid mixture in the mixing zone about the axis of the tube, which rotation is the openings 20b omitted.

Besides the causes of circulation betweena; mixing zone and the adjoining settling zone al.-.

ready considered, another cause of such circulation may be mentioned. The rotation in a-singlef direction of the stirrers involves that the distri-" bution of light and heavy liquids over the mixing zone is asymmetrical with respectto a vertical plane through the shaft of the stirring device, in

such a manner that in the horizontal :plane through the shaft the percentage of heavy liquid' in the mixture is higher on the side of the shaft where the stirrers rise than on the side where theymove downwards. The differences in pressure corresponding to this non-uniform distribution create a compensating circulation current extending through the settling zone in a horizontal plane from the opening past which the stirrers rise to that past which the stirrers move downwards. In order to avoid this undesirable circulation the outlet openings through which the mixture flows from the mixing zone to the settling zone may be displaced circumferentially in the direction of rotation of the stirring device, so that these openings come to lie at levels where the mixture in the mixing zone has practically the same composition.

A modified form of the partition wherein the outlet holes Zia" and 211) are located in this manner to avoid circulation currents due to asymmetrical distribution of light and heavy liquids is shown in Figure VIII. The direction of rotation of the shaft is indicated by the arrow. The inlet openings 20a" and 201)" are 10-" 23. cated at the top and bottom, but may be located as shown in Figure VI.

It is also possible to provide one or more openings for the passage of mixture from the mixing zone to the settling zone on one side of the shaft only. Such an arrangement is shown in Figure IX, showing the inlet openings 20a and 20b and only one group of outlet openings 2111".

Each of the figures shows only part of the complete apparatus, which may be equipped with a large number of mixing and settling zones connected in series. The apparatus in Figure I may be conceived to consist of a number of sections, separated by the walls 9, 9, etc., each of which comprises a central mixing zone and settling space on both sides thereof; one of these settling in partitions I91: and l9c are;

spaces supplies the separated A liquid treated in these sections to the adjoining section, the other settling 'zone supplies the B liquid to the other adjoining section.

The apparatus may be adapted in a known manner to the distribution of the components of a third liquid C over the two liquids A and B, which for this purpose is fed into one of the mixing zones at an intermediate point between the two ends of the apparatus.

I claim as my invention:

1. Apparatus for contacting continuously and countercurrently two at least partially immiscible liquids of diiferent densities comprising a longitudinal cylindrical shell, a plurality of partitions situated transversely to the axis of said shell subdividing the shell into a series of alternating mixing and settling zones, inlet openings in said partitions for the flow of liquid from the settling zones into the mixing zones, outlet openings in said partitions for the flow of a mixture of liquids from the mixing zones into the two settling zones, adjacent each mixing zone, a stirring device in each mixing zone mounted on a common rotatable shaft, said shaft running longitudinally through said shell, whereby said liquids can flow in opposite directions through said mixing and settling zones, and a wall in an intermediate settling zone dividing said settling zone into spaces, said wall being substantially imperforate except for openings at its outer edges, one space being in direct communication with only one of the mixing zones adjacent to the settling zone and another space being in direct communication with the other adjacent mixing zone only, and openings in said wall for the passage of. the liquids located at different levels.

2. The apparatus according to claim 1, wherein the shaft of the stirring devices is located substantially at the center of the shell and the openings in the partitions between the mixing and settling zones are situated at substantial distances from the shaft.

3. The apparatus according to claim 1, wherein the shaft of the stirring devices is located substantially at the center of the shell and the openings in the partitions between the mixing and settling zones are situated at substantial distances from the shaft, and at equal distances from the center line of the rotating shaft.

4. Apparatus for contacting continuously and countercurrently two at least partially immiscible liquids of diiferent densities comprising a longitudinal, cylindrical shell disposed in a position other than vertical, a plurality of partitions situated transversely to the axis of said shell, dividing the shell into a series of alternating mixing and settling zones, inlet openings in said partitions for the flow of liquid from the settling zones into the mixing zones, outlet openings in said partitions for the flow of a mixture of liquids from the mixing zones into the two settling zones adjacent each mixing zone, a stirrin device in each mixing zone mounted on a common rotatable shaft, said shaft running longitudinally through said shell whereby said liquids can flow in opposite directions through said mixing and settling zones and a wallin an intermediate settling zone dividing said settling zone into spaces, one space being in direct communication with only one of the mixing zones adjacent to the settling zone and another space being in direct communication with the other adjacent mixing zone only and openings in said wall for the passage of the liquids locatedat difierent levels, the openings conducting the denser liquid being situated at a lower level than the opening conducting the lighter liquid, ,said openings being at the outer edges ofsaid wall, and said wall being otherwise substantially imperforate.

5. Apparatus according to claim 4, wherein the partitions between the mixing and settling zones contain at least two outlet openings located substantially diametrically opposite to each other, one opening being slightly above and the other slightly below the level of the shaft at the position of the respective partitions.

6. Apparatus according to claim 4, wherein the outlet openings in the partitions between the mixing and settling zones are situated approximately at the level of the shaft of the stirring device at the position of the respective partitions and are provided on one side of the shaft only.

'7. Apparatus according to claim 4, wherein the outlet openings in the partitions between a mixing zone and a settling zone are shaped asradial slots radially arranged with respect to the shaft I of the stirring device.

3:- outlet conduits, said mixing zones being provided with mixing means, said inlet and outlet conduits being arranged to permit the two liquids to flow in opposite directions through said mixing and settling zones and a transverse wall, which is inclined to the horizontal, in an intermediate settling zone dividing the settling zone into two spaces, one space being in direct flow communication with only one of the mixing zones adjacent to said settling zone, and another space beingin direct communication with the other adjacent mixin zone only, openings in said. wall for the passage of the liquids, the opening conducting the denser liquid being situated atthe bottom. and the opening conducting the lighter liq- ",uid' being situated at the top of said wall, the

latter being substantially imperforate between said top andbottom.

WILLEM JOI-IANNES DOMINICUS VAN DIJCK. 

